GXB_transceivers

1 - Transcievers are enabled by creating an instance of the altgxb megafunction in your design and connecting it to an appropriate transceiver pin.

2 - The "Synopsys Constraints File" (SDC) provides Quartus with the timing constraints for your design. You must create one:

http://www.altera.com/support/software/timequest/sof-qts-timequest.html

3 - Timing models for Arria II GX are preliminary in Quartus 9.0.

4 - This error can occur if you've assigned the pin to be a differential I/O type but the pin is not actually used or connected to appropriate logic in your design (e.g. you haven't connected it to an altgxb instance).

Jake